I opened my eyes to see a clear blue sky and two men leaning over me to put a brace around my neck. I don’t know if I was already on the stretcher or if I was still on the pavement, but then there are plenty of things I don’t remember. As I would find out later, I had a brain injury.

Was I badly hurt, I asked. I felt as though someone had smashed a plank of wood across the left side of my face. The two men on either side of me carefully lifted my upper body to finish fitting the brace, giving me a view of my legs. I wiggled my left toes, which were more obliging than my lips. It couldn’t be that bad, I decided. My spinal cord still worked.

The man on my right – either an ambulance technician or a paramedic; I had no way of knowing – asked if I knew where I was. Was I … outside the Whole Foods? Did I know what happened, he asked. No. Wait … when the bronze car turned left in front of me, cutting me off, I hit the brakes on my bike. I remembered realising that it didn’t matter – I wouldn’t be able to stop in time. The next thing I remembered was the sky. I had been unconscious for about 15 minutes.

“She’s confused,” the guy on my right said to the guy on my left. I had hit my head, the maybe-paramedic told me. I had a concussion. It was a good thing I had been wearing my bike helmet. I think he said it then, but he might have said it later, in the ambulance, when he was removing my helmet. In any event, I was going to the hospital instead of my yoga class.

I spent the hours after the crash immobilised and braced, while things I didn’t fully understand happened around me. Like most writers, I am a control freak. And like most editors, I am accustomed to telling people what to do. I had the energy for neither. On any kind of normal day, this situation would have filled me with anxiety or fury, possibly both.

I was vaguely aware of being removed from the ambulance and sent into the emergency room. Then a lot of people stood around me to lift me from one stretcher to another – a surprisingly gentle operation. Later, a woman was asking me where I hurt, and I gestured to the left side of my head. My skull felt like it was trying to exit my body through the skin, pulsing routinely against the flesh of the left side of my face and my forehead. I’ll call this The Headache, and it was worse than any other headache I have ever felt. The fentanyl the doctors gave me didn’t stop The Headache, but it did succeed in making me care a lot less about it.

I noticed someone moving above me, and asked her what was happening. I was about to have a CT scan, she told me. She is the first person whose appearance I remember, even in part. She had Shirley Temple curls. I’m not sure what her face looked like, but I remember I liked her hair. I was a science journalist and had written about CT scans, but I’d never had one, I told her. So this was exciting.

But as they moved me into the scanner, I wondered: was I a science journalist? I had spoken without thinking. My entire life before the ambulance felt dim and far off. I might as well have been born on the pavement, with the neck brace half on.

I had reported on concussions, actually – particularly during the period when they were the subject of numerous lawsuits involving the US National Football League (NFL). While working at Bloomberg News I had written about the controversial diagnosis of chronic traumatic encephalopathy, or CTE, after the suicide of Junior Seau, a leading NFL player who suffered years of depression caused by repeated blows to the head. CTE, which can only be truly diagnosed after death, causes symptoms such as memory loss, depression and confusion. Scientists are now trying to find ways to make the diagnosis in living people. Multiple concussions also raise the risk of dementia, with or without CTE. It isn’t limited to football, of course – soccer players, boxers, professional wrestlers and others who participate in contact sports are also at risk – but the NFL has been at the cutting edge of the research. Former players have agitated for research on what multiple concussions do to the human brain.

The science on CTE is still in its infancy, but it is real, and a real problem, though we don’t know how widespread it is, or exactly what it means. What I quickly realised, as I lay in the hospital, is that reporting on multiple concussions hadn’t prepared me for a single one, although it was comforting that I knew what a concussion was. I’d written about the cumulative effects. I’d edited pieces about how football helmets protected players from some kinds of brain injuries but not others. I’d described symptoms of concussions. During my recovery, I began to understand the poverty of those descriptions. CTE is terrifying, but concussions themselves are bad enough.

A concussion, according the US Centers for Disease Control and Prevention (CDC), is any kind of bump or jolt to the brain that results in a change in mental status. I knew they were the most common kind of brain injury, and often associated with athletic activity. I also knew they were mild traumatic brain injuries. The CDC has estimated that the number of annual concussions in the US due to sports and other activities was as high as 3.8m. (Not every concussion results in a visit to casualty.) That, of course, doesn’t account for concussions sustained in car crashes, another common cause. In the UK, someone is admitted to hospital for a head injury once every three minutes, according to Headway, an advocacy group for brain injury. (That number includes concussions as well as more serious brain trauma.) And while American football isn’t a common cause of concussion in the UK, rugby is.

What happens with any concussion – including mine – is a recognisable set of symptoms: confusion, fatigue, difficulty remembering new information, nausea, dizziness, mood changes and sensitivity to light and sound. The number of concussions receiving medical care has been on the rise in the past few decades, in part because people are more familiar with the idea of brain injuries. Some of that increase is probably also due to the increasing athleticism of sports like football: as athletes get bigger and stronger, they’re more able to generate the kind of force that causes a concussion.

You don’t even need to be hit on the head to have one. Your brain is a gelatinous mass floating in a pool of cerebrospinal fluid inside your skull. A concussion occurs when the brain hits the skull, even if the person’s head doesn’t collide with an object. Whiplash alone can generate a concussion. After all, it doesn’t take much to deform jelly. The force of the impact with the skull can cause the brain to twist or even rebound against the other side of the skull.

The result is chaos, says John Leddy, a concussion expert at the University at Buffalo. Brain cells stretch and twist, blood vessels become leaky and the chemicals the brain uses to communicate are dumped at random into the spaces between brain cells. The electrical activity of the brain is dampened. There is a period of diminished activity from brain cells, as well as reduced blood flow in the brain, according to research on the concussion cascade.

It is a little hard to say, specifically, what happens in living brains, because brains are generally encased by skulls. Also, post-concussion chaos isn’t visible on an MRI or a CT, the two most common ways to image the brain. Scientists have tried to figure out what is going on by creating windows into animal brains by removing part of the skull, but that tends to be traumatic in its own right.

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While some scientists are pursuing blood biomarkers or eye scans as a way of diagnosing a concussion, the best way to determine if a person has a concussion is still a checklist of symptoms. This is reflected in the NFL concussion protocol, which goes into effect for any player displaying one of seven symptoms: loss of consciousness, slowness getting up, balance problems, a blank look, disorientation, clutching the head and visual facial injury. Any of those symptoms will get a player immediately removed from the field, to undergo examination by an independent neurologist.

The checklists work because concussions have predictable symptoms. Anything that requires cooperation across larger areas of the brain – balance, for example – is going to be more affected by a concussion, Leddy says. Loss of balance is a classic symptom of concussion. That is because the parts of your brain that help orient your body in space are spread throughout the jelly; your eyes, ears, muscles and joints all contribute signals, which are processed through the cerebellum, cerebral cortex and brainstem. Vision is similarly vulnerable, since control of the eye is spread throughout the brain as well. “Those are the physical signs that I look for in everybody who I see with a concussion,” Leddy says. “How their eyes are working and what their balance is like.”

Another common symptom of any brain injury, including concussion, is impaired memory. I experienced two kinds. The first, retrograde amnesia, was for events that occurred before my brain injury. I remember realising I would crash, but don’t remember the impact. The other kind, anterograde amnesia, is for events after the brain injury. This form is probably due to the chaos that was taking place inside my skull.

Lost memory is one of concussion’s hallmarks, says William Mullally, the associate chief of clinical neurology at Brigham and Women’s Hospital in Boston, and an instructor at Harvard Medical School. He’s not just familiar with concussions in the clinical sense, either: thanks to his hobbies of karate and boxing, he’s had a few himself. In one boxing match, he remembers going out to fight; then the next thing he remembers is using his opponent to pull himself up. The fight lasted three rounds, and each round was three minutes with a minute between to pause. “So that’s 12 minutes I have no recollection of,” he tells me. Apparently, he came back from having been knocked out, determined to finish the match.

Mullally tells me that these lost memories are probably the result of difficulty in the hippocampus. These small, seahorse-shaped structures – there are two in a normal brain – are very sensitive to a lack of blood flow and changes in electrical activity. Without functioning hippocampi, it’s impossible to encode short-term memories, Mullally says. And so he and I have gaps in our memory – his while boxing, and mine in the ER – from times when we were perfectly awake. Blackouts.

The next thing I rememberis being in a small room. A nurse was trying to make me comfortable. I was ravenously hungry and requested food. She nodded and left, pulling the door most of the way closed behind her. I located my phone – under the blankets with me, I discovered – and began informing people that I had inconvenienced them.

Where was my food? Suddenly, the hunger turned to nausea. I began looking for a call button, a way of alerting someone that I required a bucket. I couldn’t find it, and puked resignedly on to the floor. But even that didn’t alarm me much.

Mood changes are common with concussion, and mine started the moment I woke up. Yes, I was confused; I was also, maybe more accurately, bemused. All I needed to do was lie in bed and let people examine me. It was a lot like floating on an inner tube down a river: I remained still and the scenery changed. I mostly felt cheerful and upbeat, even though I didn’t really understand what was going on; I had at no point experienced any fear at all.

But now the people were gone, and I was alone in the room. After making a few phone calls – I wasn’t coherent company, but I still wanted to chat – I took a selfie. It was the first time I’d managed to get a look at my face: the left side was swollen, my lips were busted and bloody. My chin was scraped, as was my nose. My left eye was at half-mast, but overall, it was fine. Aside from all that, my eyebrows and hair looked great.

It wasn’t until my boyfriend arrived that I really began to understand that I was seriously injured. Immediately after getting a good look at me, he sat down on the floor and put his head between his knees. My face was so disturbing that he had nearly fainted.

Joe Selkirk and Yuri Pompilio during a light-middleweight contest in 2015. Boxers are particularly at risk of concussion. Photograph: Alex Livesey/Getty

After he had recovered from the shock, I made the first catalogue of my injuries. My face hurt, of course, but so did my left shoulder, hip and knee. All would later produce Technicolor bruises. I had chipped a tooth. That was it. Most of the damage was on my face. I must have landed directly on my head.

When I stood up for the first time since the crash, I found that standing made the headache worse. I began to shuffle toward the restroom under a nurse’s supervision. The bathroom couldn’t have been more than 20 feet away, but it still took me quite some time to reach it. I had only the vaguest sense of where my limbs were and whether or not my feet were correctly aligned with the floor. My body had become a clumsy mecha suit, and I was trapped inside, trying to operate what felt like a large hunk of metal.

Things happened quickly after I demonstrated I could walk under my own power: a doctor came in to summarise what they had found (concussion, nothing more serious) and give me various prohibitions: no TV, no alcohol, no reading, no internet. Then I was discharged. We went home in a cab big enough to hold the two of us and my crumpled bike. I figured my recovery would take about a week. I was wrong.

I alarmed people pretty much every timeI mentioned my concussion. The actual injury might not have been scary to me, but it scared everyone around me. The brain lives pretty close in our imaginations to the self. It is one of the reasons some people locate the self specifically as the brain, and probably why people cryogenically freeze their heads. It is there in the hopes of the Italian surgeon who promises that he will perform a full “brain transplant” in the near future. This belief is probably why brain injuries scare people.

And so we have come to a scary phrase: “personality change”. I had one. They’re common with brain injuries, including concussion.

Personality is a major part of how we understand ourselves; in fact, we use it as a reference for famous people – a television personality. To have your personality altered by brain trauma seems to upset people more than having it altered by, for instance, emotional trauma. I don’t know why this is. But everyone’s personality changes over the course of a lifetime, usually gradually. Perhaps it’s the suddenness of the personality change that frightens people, or perhaps it raises scary questions about identity.

I’m a pessimist, the person who is useful in the worst-case scenario because they are the only one who planned for it. Or rather, I was a pessimist before I hit my head; I am slowly returning to it now. But I spent about a month after the crash incapable of doing anything other than looking on the bright side.

I still felt like myself, but it was as if my personality was a set of piano keys, and someone had sliced off all the notes you’d ordinarily play with your left hand. I could go on playing with both hands, but only the top half of the keyboard was available. While I was in the ER, it occurred to me: what if I am stuck like this for ever? I considered it, and then decided: “Well, I’d have to quit my job, which is a shame because I like it. But there would probably be another job I could do. Anyway, it’s a concussion, and I’m going to recover.” Then I felt satisfied and closed my eyes for a nap.

If I thought that I was my brain, I probably would have found the injury more upsetting. But I didn’t and don’t believe that; my self is an interaction between my body and my brain. In his 1984 book A Leg to Stand On, the neurologist and author Oliver Sacks wrote about the time he injured his leg skiing and required surgery. After surgery, his leg no longer felt like his own. “I could no longer remember having a leg,” he wrote. “I could no longer remember how I had ever walked and climbed.” An injury to his body changed his mind. The brain alone, then, can’t be the reservoir of self; a brain injury might alter me, but it doesn’t annihilate myself any more than a broken leg would.

Courtney Lawes after colliding with All Black Sam Whitelock during a rugby match at Twickenham in 2014. The England player had to leave the field with a concussion. Photograph: Tom Jenkins for the Guardian

The mood change did make memory lapses easier to endure, though. I had always been bad with names, but I was noticeably worse: no new names stuck. I often experienced “tip-of-the-tongue syndrome”, when I’d know there was a word I specifically wanted but couldn’t remember what it was. “Boat farm” meant marina, “salad with tomatoes, mozzarella and basil” got me caprese, and “circular reasoning where you say the same thing twice” is tautological. It was like a guessing game in which even I didn’t know the word people were trying to guess, and I played with whoever was around me until I found the word I was looking for. Viewing it as a game made it less frustrating and a little more fun, so I chose to do that.

I started writing again about two weeks after I hit my head, which is the longest I’ve gone in my adult life without writing. That diary entry shows more cross-outs and uncertain spellings than any of the previous ones. As I continued writing, the number of cross-outs and bum spellings declined. But it was clear: there was a before, and there was an after.

My personality change – the loopy good mood, the entirely unfounded sense of wellbeing – isn’t something any of the experts I spoke to run into that often. What are more common, and tend to be listed in the literature on concussion, are two things: anxiety and depression. But the brain-body connection is relevant here, too. Most concussion patients have difficulty with light and noise; they often isolate themselves in dark, quiet rooms in response. In people without concussion, this kind of behavior creates depression and anxiety. So, did the depression and anxiety come from the brain injury, or the self-imposed isolation afterward?

For a long time, doctors thought that patients needed to rest totally after a concussion until all symptoms were relieved, Leddy says. “For example, you take an adolescent athlete and tell him or her to do nothing for weeks. Well, they’re used to doing things, you know, being at school,” he says. “We know that if you take someone like that who doesn’t have a concussion and tell them not to do anything, they get symptoms. They get anxious, and some get depressed and irritable.” That’s why concussion patients are encouraged to get back into activities when they start to feel able to, and to take it gently, he says. “We think that’s a better way for the brain to recover.”

The symptoms can come from other places, too, former NFL player Ben Utecht told me. He’s the author of a book called Counting the Days While My Mind Slips Away, which he wrote in order to preserve his memories. He had had five documented concussions between college football and professional play. Recovery was different each time, though he never experienced chronic headaches. Light sensitivity, though – that he remembers. “The consequences I faced got worse with each concussion I sustained,” he told me. After the fourth concussion, he was diagnosed with amnesia. That recovery process was different because it was more severe.

The biggest changes that concussion caused for Utecht were cognitive: he struggled with the skills we rely on to manage time and pay attention, called executive function, and his memory deteriorated. When Utecht joined the Cincinnati Bengals, learning their offensive system of play was even harder. He received his final concussion during training in 2009; after that, he ended his football career. His mood tanked: he was depressed and anxious, and his patience was nonexistent. “But I had just walked away from a game I had played for 20 years,” he said. “How much of that is just life?”

What improved his mood, he told me, was an intensive brain-training programme. He describes cognitive fitness training as “my miracle story”. While he had taken it to boost his memory, he discovered he was less irritable as his memory improved. Having a hard time remembering his calendar, remembering names and remembering the right words made things more frustrating. “I think that frustration plays a role in stress, and lack of patience,” Utecht says. “Because nothing else changed in my life but this cognitive training.”

There is no treatment for concussionexcept for patience and time, but people seem not to believe that. Well-meaning friends suggested I supplement with omega-3 fatty acids and eat extra protein. There is no evidence that either makes a difference for concussion. Some people recover quickly, taking only days to feel normal. About one in five concussion patients take weeks or months to recover. I was one of those patients. How severe the injury was has little to do with how long it takes to recover; women, younger people, those who’ve had concussions before and people with other brain disorders are more likely to take longer, according to Leddy’s research.

“I always tell my patients that I don’t have a crystal ball,” says Alicia Sufrinko, a concussion specialist at University of Pittsburgh. “I’m not going to be able to forecast this.” Some people have stronger systems for balance than others; some have better visual systems. But the wider environment also makes a difference, she says. Social factors matter. Loneliness and isolation make recovery harder.

I didn’t lack company, but I had a hard time staying awake to hang out – I spent most of the first week after the injury asleep. I still had the headache, and being asleep meant I didn’t feel it; it was my constant companion for a week. But also, every time I woke up, I felt a little better: my balance had improved slightly, for instance, and it was easier for me to think. For the first week after the crash, I kept the curtains drawn in my apartment and didn’t turn the lights on until I absolutely had to.

Even for people who feel normal, things aren’t back to normal in the brain, Harvard’s Mullally tells me. Studies in humans and in animal models show unusual patterns of blood flow in the brain persist for a month. Gentle cardio exercise – such as walking – can help improve it. A concussion patient shouldn’t go back to full steam ahead immediately, but neither should they wait until they are well to begin resuming their lives, he says.

Even after the headache finally vanished, bright light and loud sounds could trigger smaller, migraine-like ones, so I wore sunglasses every time I left the house. I also carried earplugs with me, just in case. Before the crash, I hadn’t noticed how loud everything was; now I was painfully aware. Coffee shops (high ceilings, cement floors and exposed tile), airports (high ceilings, hard surfaces, intercoms, inconsequential beeping), and public transit (the screeching of a train on the track) all guaranteed headaches. The sensitivity to noise lasted for about three weeks, and it was isolating. I often left the apartment with earplugs in. The world isn’t designed for brain injuries. Basically, Mullally told me, almost everything is brighter and louder than we realise. Our brains filter a lot of stuff out, but my brain couldn’t do that filtering.

After a week in bed, I got restless. I started with a half an hour of walking, and when that didn’t make me tired, I moved up to an hour. Doing too much, of course, could mean a headache. That was the worst period of my recovery. By the second week, my black eye was gone and my lips weren’t split anymore, but stairs and curbs – anything that required stepping down – were still terrifying. I didn’t feel normal, but I looked normal. And that meant people treated me like I was normal. Our society really isn’t equipped for people with brain injuries, which are real but invisible. Even though I knew my balance wasn’t good enough to stand on public transport, I was scared to ask for a seat on a crowded train. An injury no one can see doesn’t inspire sympathy.

After a month, I felt confident enough to go back to yoga, where I discovered my balance was still bad; easy one-legged poses I had considered the base of my practice were gone. I could walk and even bike just fine, but the subtleties of positioning my body in space hadn’t returned.

That was also around the time I went back to work. I still got tired quickly, and my day often ended earlier than I wanted – usually with a headache. But working helped with my memory, too. Things that had happened to me before the concussion still had a patina of unreality to them, because I couldn’t feel the memories. I quickly discovered that while the content of my memory was intact, the emotions associated with the memories were gone.

Fortunately, memories aren’t static. Every time you or I recall a memory, we repaint it in our minds. Our memories change every time we pull them forward. And so, back at work, I began to recompile memories of my pre-concussion life. After a few weeks, most of my memories again had emotions associated with them.

There were the little victories. The first day I was back at work, I told a writer her story had an unclear antecedent; I was immediately filled with glee that I not only had noticed, but had selected the right word. Something in the familiar process of editing had called them forth – and remembering them was akin to finding an unexpected $20 bill in an old pair of jeans.

There were also little losses. For example, it became apparent, once I was back at work, that my attention span wasn’t what it had been. This is actually common in concussion patients, says Sufrinko. It’s related to the problems with vision, which makes sense, since attention and vision have a lot to do with each other. Vision steers attention in ways most of us aren’t aware of, she says. “If you’re daydreaming and you’re off in your own little land, and then all of a sudden you realise you’re not paying attention, you also realise that visually you’re not focused,” she says. “People with visual problems lose their attention a lot.”

But this distractibility also faded. My balance improved. Finally, the only thing left was fear. For weeks, sound and light gave me headaches. When it stopped, I still avoided music, TV and movies. I felt actual dread about them. I worried I’d screw up something serious at work if my attention drifted. And steep downhill slopes or uneven stairs filled me with gut-level terror. It didn’t matter that I navigated stairs and slopes as well as I had before. My confidence was gone.

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I had learned to avoid certain things, I realised. A month is plenty of time to be conditioned to fear my headache triggers: complex tasks, sound, bright lights, tests of my balance. Was this was the anxiety that had been mentioned in the medical literature? But my fears were conditioned; I had learned to fear The Headache. That was good news, I figured, since conditioned fear could be extinguished. The trick was to re-expose myself to the things I now feared, starting slowly and gently: Bruce Brubaker’s Glass Piano. Half a television show. A yoga class. Backpacking for days in a redwood forest on a mostly downhill route. Writing this article.

Structurally, as a writer, I want to put some kind of moral here to send my reader off happy. I actually spent weeks thinking: what is the lesson? As far as I can tell, there is no lesson. Brain injuries happen for no reason, after all. Even when I found it difficult to think straight, I didn’t feel much of a loss. In any event, I have bought a new bicycle and a new helmet. I’ve been riding my bike to yoga class for the last few months, and I have successfully arrived every time.